As of now, Bitbucket Server allows merge checks based on build status of source branch(es). This functionality is not available for target branch of a PR.
More detail from a customer (emphasis mine):
During Pull request creation, we are using hook "Minimum successful builds" which reads the build status of branches and allows merge of feature to master if feature has at least one successful build.
We want to enable hook for master branch where feature/other branches can merge to master only when master has at least 1 green/successful build.
There is no marketplace app either that addresses this functionality.